Developing Fe/zeolite catalysts for efficient catalytic wet peroxidation of three isomeric cresols

Five Fe/zeolite (i.e., Fe/ZSM-5-1, Fe/ZSM-5-2, Fe/ZSM-5-3, Fe/MCM-22, and Fe/MOR) were prepared and tested as catalysts in the catalytic wet peroxide oxidation process (CWPO). Their adsorption and catalytic effects on the removal of three isomeric cresols were systematically explored. Sufficient characterizations were carried out to illuminate the iron species dispersed on the catalysts' surface porous channels. Other properties of the catalysts such as the Si/Al ratio, crystalline structures, and morphologies were systematically studied. After loaded with iron, the catalysts maintained zeolite's framework, which possessed specific porous structures and surface areas. Interestingly, the Si/Al ratio seemed to be an important issue influencing the adsorption and catalytic degradation of cresols due to n-π interaction and the acceleration of HO• generation, respectively. The amount of framework-Fe and Fe³⁺Al-Si in Fe/ZSM-5-3 was the most, which was crucial for its better catalytic ability than the other Fe/ZSM-5 catalysts (71.19% for m-cresol conversion). In conclusion, the catalytic activities of all the Fe/zeolites followed the sequence: Fe/ZSM-5-3> Fe/ZSM-5-2> Fe/ZSM-5-1> Fe/MCM-22>Fe/MOR. For three cresols, m-cresol was more susceptible to the attack of HO• than p- and o-cresol because more positions of m-cresol could be easy to be approached by the oxidizing agent. Considering the mild reaction condition in this study, such as 30 °C, pH=4.0, and catalyst dosage=1.0 g/L, the Fe/ZSM-5-3 was a promising zeolite catalyst for the degradation of refractory contaminants in practical wastewater.